US2024393224A1PendingUtilityA1
Flexible wall device and method for measuring gas permeability coefficient and gas diffusion coefficient of soil
Est. expiryMay 22, 2043(~16.8 yrs left)· nominal 20-yr term from priority
G01N 15/0826G01N 15/0806G01N 33/246G01N 33/24G01N 2013/003G01N 13/04
62
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Claims
Abstract
A flexible wall device and method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil includes a gas washing device, a confining pressure-volume change system, a drying-wetting cycle control system and a gas measuring device. The drying-wetting cycle control system includes a humidity controller and valves. The gas measuring device includes a top lid, a cylindrical wall, a base, an upper chamber and a lower chamber. The top lid, the cylindrical wall and the base are connected by bolts and nuts, and the base has four passages, which are respectively connected to the gas washing device, the confining pressure-volume change system, the drying-wetting cycle control system and the gas measuring device, between the base and top lid are sequentially arranged from bottom to top as the lower chamber, lower perforated plate, lower permeable stone, sample, upper permeable stone, upper perforated plate, upper chamber, and control rod.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, comprising a gas washing device, a confining pressure-volume change system, a drying-wetting cycle control system and a gas measuring device; wherein the gas washing device comprises a high-purity nitrogen cylinder, a pressure reducing valve, a pressure regulating valve and a steady-flow valve; the confining pressure-volume change system comprises an air compressor, a first pressure regulating valve, a second pressure regulating valve and a volume change measuring tube; the drying-wetting cycle control system comprises a humidity controller, a first humidity controller valve and a second humidity controller valve; the gas measuring device comprises a top lid, a cylindrical wall, a base, an upper chamber and a lower chamber, wherein the top lid, the cylindrical wall and the base are connected by bolts and nuts, and the base has four passages, wherein the four passages are respectively connected to the gas washing device, the confining pressure-volume change system, the drying-wetting cycle control system and the gas measuring device; between the base and the top lid are sequentially arranged from bottom to top as the lower chamber, a lower perforated plate, a lower permeable stone, a sample, an upper permeable stone, an upper perforated plate, the upper chamber, and a control rod.
2 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 1 , wherein the top lid, the cylindrical wall and the base enclosing a pressure chamber; the four passages of the base are respectively an air inlet passage, an air outlet passage, a water inlet passage and a base passage, wherein an air inlet end of the air inlet passage is connected to the gas washing device, and an air outlet end of the air inlet passage is connected to the upper chamber; an air inlet end of the air outlet passage is connected to the upper chamber, and an air outlet end of the air outlet passage is connected to the drying-wetting cycle control system; a water inlet end of the water inlet passage is connected to the volume change measuring tube, and a water outlet end of the water inlet passage is connected to the pressure chamber; a first end of the base passage is connected to the lower chamber, and a second end of the base passage are respectively connected to the drying-wetting cycle control system and the confining pressure-volume change system.
3 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 2 , wherein the high-purity nitrogen cylinder is equipped with the pressure reducing valve, the pressure reducing valve is connected to the pressure regulating valve and the steady-flow valve arranged in series, and the steady-flow valve is connected to the air inlet end of the air inlet passage on the base.
4 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 2 , wherein the humidity controller of the drying-wetting cycle control system is connected to the base passage at a first end and the air outlet passage at a second end, the first humidity controller valve is installed between the air outlet passage and the humidity controller, and the second humidity controller valve is installed between the base passage and the humidity controller.
5 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 2 , wherein an output end of the air compressor is connected to the first pressure regulating valve and the second pressure regulating valve set in parallel, an output end of the first pressure regulating valve is connected to a first end of the volume change measuring tube, a second end of the volume change measuring tube is connected to the water inlet end of the water inlet passage of the base, and the water inlet passage is connected to the pressure chamber; an output end of the second pressure regulating valve is connected to the base passage of the base in turn via a U-shaped pressure measuring tube, a gas sampling port and a second capillary tube, the base passage leads to the lower chamber, and the second pressure regulating valve is used to regulate a gas pressure in the lower chamber.
6 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 2 , wherein an exhaust valve and the control rod connected to a perforated loading plate at one end are formed at the top lid, the control rod rotatably runs through a top of the top lid and the upper chamber, and the perforated loading plate is connected to a lower end of the control rod and is located inside the upper chamber; a bottom of the upper chamber is sequentially equipped with the upper permeable stone and the upper perforated plate from the bottom to the top, a piece of perforated silicone gasket is formed between the upper perforated plate and the perforated loading plate, and opening specifications of the perforated loading plate, the perforated silicone gasket, and the upper perforated plate are exactly same, the perforated silicone gasket and the upper perforated plate are tightly bonded and placed according to an overlap of opening parts, and the two openings do not block each other; a top of the lower chamber is equipped with the lower perforated plate and the lower permeable stone from bottom to top, a foundation is formed at a bottom of the lower chamber, and the upper chamber and the lower chamber have a same internal net height.
7 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 6 , wherein the control rod seals a first sealing ring and the top lid through a first nut, and the control rod seals a second sealing ring and the upper chamber through a second nut.
8 . The flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 2 , wherein a side-wall of the upper chamber is provided with two openings, and the two openings are connected to an air inlet pipe and an air outlet pipe; the air inlet pipe is connected to the air inlet passage of the base, the air outlet pipe is connected to the humidity controller, an electronic soap film flowmeter and a first capillary tube in turn through the air outlet passage, and a droplet is injected into the first capillary tube.
9 . A method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, comprising employing the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 1 , comprising the following steps:
step 1, preparation of sample: the soil to be measured is dried, crushed and sieved through a 2 mm sieve, the soil is adjusted to a target moisture content, and then compacted in layers with molds according to a target dry density, and an inter-layer interface is scraped; step 2, install the sample: place the lower chamber, the sample, and the upper chamber on a surface of the foundation from bottom to top, and paste a thin layer of Vaseline to outer walls of the foundation, the lower chamber and the upper chamber, and then wrap a latex film on sidewalls of the foundation, the lower chamber, the sample and the upper chamber, and finally fix the two ends of the latex film on the foundation and the upper chamber respectively with first O-rings and second O-rings, and then immediately followed by fixing and sealing the cylindrical wall, the base, and the top lid with nuts and bolts; open the exhaust valve, adjust the first pressure regulating valve, and apply a certain air pressure to the volume change measuring tube, leading to water go through the pipeline into the pressure chamber, until the exhaust valve discharges water and no air bubbles, close the exhaust valve; adjust the first pressure regulating valve, and apply a certain confining pressure (10-20 kPa) to the sample; step 3, flush the upper chamber: close all the valves, rotate the control rod, so that apertures on the perforated loading plate and the upper perforated plate just misaligned with each other, to isolate gas of the upper chamber from entering the sample through the upper perforated plate, and then open the high-purity nitrogen cylinder and the valve of electronic soap film flowmeter, control the inlet flow rate through an adjustment of the pressure regulating valve and the steady-flow valve, and the gas flows into the upper chamber through the air inlet pipe, and is discharged into the atmosphere through the air outlet pipe; after 8-10 minutes, close the pressure reducing valve of the high-purity nitrogen cylinder and the valve of electronic soap film flowmeter to stop the nitrogen input; step 4, open the first capillary valve and the second capillary valve, rotate the control rod, so that the perforated loading plate and the upper perforated plate connect with each other through their respective openings, and the gas in the upper chamber flows through the upper perforated plate into the sample, and immediately start the timer, this time t=0, and then determine the concentration of oxygen in the lower chamber over time through the gas sampling port, which is connected to the lower chamber, for the sample with the degree of saturation <85%, an oxygen concentration in the lower chamber is measured in minutes as a time scale, and for the sample with the degree of saturation ≥85%, the oxygen concentration in the lower chamber is measured on a time scale of hours; step 5, the following theoretical equation was derived from Fick's law and is used to best-fit the oxygen concentration in the lower chamber with respect to time to determine the gas diffusion coefficient D p :
D
P
=
-
3
H
2
Lt
[
ln
B
-
ln
A
+
ln
(
H
2
H
+
2
L
ε
-
C
t
C
0
)
]
3
H
-
L
ε
(
1
)
wherein
:
A
=
-
L
ε
H
-
2
L
2
ε
2
3
H
2
(
2
)
B
=
(
L
ε
H
-
L
2
ε
2
3
H
2
)
(
5
L
ε
3
H
+
2
)
+
L
3
ε
3
H
3
+
L
2
ε
2
H
2
(
3
)
wherein: t is the time; L is half of a height of the sample; H is the internal net height of the upper chamber; C 0 and C t are the oxygen concentration in the lower chamber at the beginning and the oxygen concentration in the lower chamber at the time of t, respectively; ε is the gas-filled porosity of the sample;
step 6, the measurement of gas permeability coefficient: close the first capillary valve and the second capillary valve, open the valve of the U-shaped pressure measuring tube and valve of electronic soap film flowmeter, open the air compressor, adjust the inlet pressure through the second pressure regulating valve to apply a constant air pressure in the lower chamber, when the U-shaped pressure measuring tube readings become stabilized, record the U-shaped pressure measuring tube and electronic soap film flowmeter readings;
step 7, the inlet pressure is changed to obtain the gas flow rates at three different air pressures, and the gas permeability coefficient of the soil sample is calculated according to the following equation derived based on Darcy's law:
k
a
=
μ
Qh
S
Δ
P
(
4
)
where S is a cross-sectional area of the sample; ρ is a viscosity coefficient of the gas; ΔP is a pressure difference between the two ends of the sample; h is the height of the sample; Q is an outflow rate of the gas;
step 8, close the valve of the U-shaped pressure measuring tube and valve of electronic soap film flowmeter, open the first humidity control valve and the second humidity control valve, adjust the humidity controller according to the target moisture content, and control the gas flow of constant humidity through the sample, equilibrate for 8-10 days, and repeat step 4 to step 7, the gas permeability coefficients and the gas diffusion coefficients of the soil samples of different moisture contents are obtained; after each drying and wetting cycle, the volume change measuring tube readings are recorded, and the volume change of the sample is obtained.
10 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 9 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, the top lid, the cylindrical wall and the base enclosing a pressure chamber; the four passages of the base are respectively an air inlet passage, an air outlet passage, a water inlet passage and a base passage, wherein an air inlet end of the air inlet passage is connected to the gas washing device, and an air outlet end of the air inlet passage is connected to the upper chamber; an air inlet end of the air outlet passage is connected to the upper chamber, and an air outlet end of the air outlet passage is connected to the drying-wetting cycle control system; a water inlet end of the water inlet passage is connected to the volume change measuring tube, and a water outlet end of the water inlet passage is connected to the pressure chamber; a first end of the base passage is connected to the lower chamber, and a second end of the base passage are respectively connected to the drying-wetting cycle control system and the confining pressure-volume change system.
11 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 10 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, the high-purity nitrogen cylinder is equipped with the pressure reducing valve, the pressure reducing valve is connected to the pressure regulating valve and the steady-flow valve arranged in series, and the steady-flow valve is connected to the air inlet end of the air inlet passage on the base.
12 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 10 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, the humidity controller of the drying-wetting cycle control system is connected to the base passage at a first end and the air outlet passage at a second end, the first humidity controller valve is installed between the air outlet passage and the humidity controller, and the second humidity controller valve is installed between the base passage and the humidity controller.
13 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 10 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, an output end of the air compressor is connected to the first pressure regulating valve and the second pressure regulating valve set in parallel, an output end of the first pressure regulating valve is connected to a first end of the volume change measuring tube, a second end of the volume change measuring tube is connected to the water inlet end of the water inlet passage of the base, and the water inlet passage is connected to the pressure chamber; an output end of the second pressure regulating valve is connected to the base passage of the base in turn via a U-shaped pressure measuring tube, a gas sampling port and a second capillary tube, the base passage leads to the lower chamber, and the second pressure regulating valve is used to regulate a gas pressure in the lower chamber.
14 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 10 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, an exhaust valve and the control rod connected to a perforated loading plate at one end are formed at the top lid, the control rod rotatably runs through a top of the top lid and the upper chamber, and the perforated loading plate is connected to a lower end of the control rod and is located inside the upper chamber; a bottom of the upper chamber is sequentially equipped with the upper permeable stone and the upper perforated plate from the bottom to the top, a piece of perforated silicone gasket is formed between the upper perforated plate and the perforated loading plate, and opening specifications of the perforated loading plate, the perforated silicone gasket, and the upper perforated plate are exactly same, the perforated silicone gasket and the upper perforated plate are tightly bonded and placed according to an overlap of opening parts, and the two openings do not block each other; a top of the lower chamber is equipped with the lower perforated plate and the lower permeable stone from bottom to top, a foundation is formed at a bottom of the lower chamber, and the upper chamber and the lower chamber have a same internal net height.
15 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 14 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, the control rod seals a first sealing ring and the top lid through a first nut, and the control rod seals a second sealing ring and the upper chamber through a second nut.
16 . The method for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil according to claim 10 , wherein in the flexible wall device for measuring gas permeability coefficient and gas diffusion coefficient of unsaturated soil, a side-wall of the upper chamber is provided with two openings, and the two openings are connected to an air inlet pipe and an air outlet pipe; the air inlet pipe is connected to the air inlet passage of the base, the air outlet pipe is connected to the humidity controller, an electronic soap film flowmeter and a first capillary tube in turn through the air outlet passage, and a droplet is injected into the first capillary tube.Join the waitlist — get patent alerts
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